In a composting toilet the toilet waste, i.e. urine, faeces, and toilet paper, is composted into humus with the aid of biological microorganisms and evaporation of liquids. To accelerate the decomposition process, controlled supply of heat and air and stirring of the compost at regular intervals may be resorted to.
For various reasons, primarily the frequency of use of the composting toilet, the times of use and the number of users, the compost often tends to be either too moist or too dry. In both cases, the decomposition process is decelerated and may even stop completely. The compost is too moist when it is no longer able to absorb liquid; the liquid remains on top of the compost and slowly seeps into the humus-collection container. As a result, the humus-collection container risks being filled with liquid and liquid may even spill over, which may result in damage due to damp and cause bad odours. Reversely, the compost is too dry, when lumps form or when toilet paper remains on top and is not soaked-through or mixed with the rest of the material upon stirring. The composting or decomposition process can then be slowed down or stop completely. If this happens, liquid must be supplied, for example by water being sprayed thereon one or several times until the compost becomes sufficiently moist for the decompostion process to proceed as intended.